This application claims priority from Korean Patent Application No. 2001-14004, filed on Mar. 19, 2001, the contents of which are incorporated herein by reference in their entirety.
1. Field of the Invention
The present invention relates to a semiconductor device and method of forming the same, and more particularly to a semiconductor device having a silicide thin film and method of forming the same.
2. Description of the Related Art
Silicon generally has the properties of semiconductor, but acts as a conductor when impurities are implanted into it, as is the case when used in a semiconductor device. In addition, silicon and metal can be easily transformed into a metal silicide having high conductivity. Accordingly, in a highly-integrated semiconductor device in which resistance increases as the width of a conductive line such as a gate line and contact sizes are reduced, metal silicide is often used to form a portion of a contact interface or a signal line such as the gate line to enhance the conductivity and the performance of the device.
Also, as semiconductor devices are scaled down, the junction depths of source/drain regions are also reduced. To reduce the contact resistance of the source/drain regions, metal silicide can again be used. At this time, a layer of metal silicide is generally formed to a thickness of several hundred angstroms (xc3x85). However, for example, when the metal silicide layer having a thickness of 300 xc3x85 is formed on the source/drain regions having a thin junction depth of 1000 xc3x85, the metal silicide layer may be directly connected to the substrate beyond the source/drain regions. Consequently, various problems, such as a junction spiking phenomenon generating a leakage current, can occur. This junction spiking phenomenon is similar to the spiking problem in which the signal current leaks into the substrate when aluminum contact plugs are connected to the source/drain regions.
Cobalt or titanium (Ti) metals, having a low contact interface resistance such as are commonly used to form the metal silicide layer. With cobalt, however, the probability of encountering the junction spiking phenomenon is increased. The cobalt silicide layer is usually formed by coating a cobalt layer on the exposed surface of a substrate through sputtering. Sputtering is followed by a two-step heat treatment, in which a first step takes place at temperatures of 500 to 600xc2x0 C. and a second step takes place at more than 750xc2x0 C., or a one-step heat treatment that takes place at a high temperature of more than 750xc2x0 C. The heat treatment silicifies the cobalt layer. After the heat treatment, non-reacted portions of the cobalt layer are removed in a self-aligned manner by wet etching. Using this technique, it is difficult to control a speed of forming the cobalt silicide layer to form a thin layer. When the cobalt silicide layer is formed, the polysilicon layer and the cobalt layer are usually combined in a ratio of 360 xc3x85 to 100 xc3x85. It is further difficult to coat the cobalt layer uniformly at a thickness of less than 80 xc3x85 through sputtering and to re-form it repeatedly. The reliability of fabrication process is therefore deteriorated. Thus, forming the cobalt silicide layer of less than 300 xc3x85, as well as preventing the junction spiking phenomenon in the source/drain regions having the thin conjunction depth, is difficult.
When the signal current leaks into the substrate without being transmitted through channels, the consumption of the signal current is increased and the operation speed of transistors slows. Worst yet, the transistors may not operate properly. Particularly, in a low power SRAM device, it is necessary to prevent the generation of leakage current to obtain reliable operation of the device.
To prevent the spiking phenomenon that results from using the cobalt silicide layer, a titanium silicide layer (TiSi2) in the source/drain regions can be formed using titanium to reduce the spiking phenomenon. In this case, however, because titanium exhibits an amount of resistance that depends on the line width, the resistance is abruptly increased in most semiconductor devices having a line width of less than 0.2 xcexcm. Also, the resistance characteristics of the titanium may be degraded following heat treatment.
According to an aspect of the present invention, a semiconductor device comprises a gate insulation layer formed on an active region of a semiconductor substrate. A gate electrode is formed on the gate insulation layer. An impurity region such as a source/drain region is formed in the active region adjacent the gate electrode. A silicide thin film is formed to a thickness of less than approximately 200 xc3x85 in the impurity region.
According to another aspect of the present invention, there is provided a method of forming a semiconductor device comprising forming an isolation layer on a surface of a substrate to define an active region, forming at least one gate electrode by sequentially forming a gate insulation layer and a gate layer on the surface of the substrate in the active region and patterning them to expose source/drain regions, forming a metal layer such as a cobalt layer on the surface of the substrate in the exposed source/drain region, forming a low temperature type silicide thin film such as a cobalt silicide thin film by performing a heat treatment at a low temperature of 150 to 450xc2x0 C., preferably 300 to 400xc2x0 C. to the substrate on which the cobalt layer is formed, removing non-reacted portions of the cobalt layer from the substrate on which the low temperature type cobalt silicide thin film is formed, and forming a high temperature type metal silicide thin film such as a high temperature type cobalt silicide thin film by performing a heat treatment at a high temperature of more than 700xc2x0 C., preferably 850xc2x0 C. to the low temperature type silicide thin film.
In the invention, because the heat treatment after forming the cobalt layer is carried out at a low temperature, it is desirable that the low temperature type cobalt silicide thin film be formed in an in-situ method in a sputtering device after the sputtering. Also, instead of the cobalt layer, a layer of metal such as nickel, titanium and platinum can be used.